LightDM and GDM fail to start after update in virtualbox-guest-x11

[Shepherd King]

1) Output of lsb_release -rd:
Description: Ubuntu 16.04.4 LTS
Release: 16.04

2) Output of apt-cache policy lightdm:
lightdm:
  Installed: 1.18.3-0ubuntu1.1
  Candidate: 1.18.3-0ubuntu1.1
  Version table:
 *** 1.18.3-0ubuntu1.1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
        100 /var/lib/dpkg/status
     1.18.1-0ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

3) What I expected to happen:
- Expected the display manager to take me to the lightdm user login screen.

4) What happened instead:
- lightdm made 5 attempts to start before failing. Failure messages were "failed to start Detect the available GPUs and deal with any system changes" and "Failed to start Light Display Manager".

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm 1.18.3-0ubuntu1.1
ProcVersionSignature: Ubuntu 4.4.0-116.140-generic 4.4.98
Uname: Linux 4.4.0-116-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl wl
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
Date: Sat Mar 31 17:43:08 2018
InstallationDate: Installed on 2015-11-23 (859 days ago)
InstallationMedia:

ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/zsh
SourcePackage: lightdm
UpgradeStatus: Upgraded to xenial on 2017-01-18 (437 days ago)

[Shepherd King (shellcat-zero)]

This was a system that generally stayed on 24/7, so I am not sure what updates might have caused this to happen. The last update before the system rebooted occurred at "Start-Date: 2018-03-31 09:57:33", see attached update history file.

I should also add that I have been using lightdm along with LXDE on this system. When the error originally occurred, another failure message was "lightdm: PAM unable to dlopen(pam_kwallet.so): /lib/security/pam_kwallet.so: cannot open shared object file: No such file or directory" so I then proceeded to install libpam-kwallet4 and libpam-kwallet5 (as you can see in the install history), which made that error go away, but the lightdm startup problem persisted. I then attempted to install and use gdm, but it failed as well. I then tried lxdm and it succeeded, except that there were many applications that could not be launched once logged into the environment. I believe the problem has something to do with lightdm and gdm not being able to unlock a keyring of some sort, but I don't see libpam-kwallet4 or libpam-kwallet5 mentioned as dependency for it.

[Shepherd King (shellcat-zero)]

With libpam-kwallet4 and libpam-kwallet5 removed, I've attached the output of "journalctl -p err -b -r" for you to inspect as well, see journalerrs.log.

[Shepherd King (shellcat-zero)]

Based on the discussion from https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1309535, libpam-kwallet errors appear to be a non-issue in this case. I am still unsure as to why lightdm and gdm are failing but lxdm succeeds albeit with a now-crippled desktop environment. The gdm failure messages appeared to be much less helpful, something to the effect of: "CRITICAL: We failed, but the fail whale is dead".

[Shepherd King (shellcat-zero)]

See additional logs files attached. This is a hybrid Intel/AMD system, but the Intel graphics is the only one used as far as I know:

% lspci -nnk -d ::0300
00:02.0 VGA compatible controller [0300]: Intel Corporation 4th Gen Core Processor Integrated Graphics Controller [8086:0416] (rev 06)
 DeviceName: Onboard IGD
 Subsystem: Dell 4th Gen Core Processor Integrated Graphics Controller [1028:05cc]
 Kernel driver in use: i915
 Kernel modules: i915
01:00.0 VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] Venus XT [Radeon HD 8870M / R9 M270X/M370X] [1002:6821] (rev ff)
 Kernel driver in use: radeon
 Kernel modules: radeon

[Shepherd King (shellcat-zero)]

Here is also the boot history, to match against the software install/update history log that I attached earlier. The issue occurred on the first reboot on March 31st, the prior successful reboot was March 13th. The history.log file shows updates to systemd and openbox on March 25th that may be relevant to this issue, but I do not know what else to do to investigate the underlying cause.

% last reboot -f wtmp.1
reboot system boot 4.4.0-116-generi Sat Mar 31 18:35 still running
reboot system boot 4.4.0-116-generi Sat Mar 31 10:06 still running
reboot system boot 4.4.0-116-generi Sat Mar 31 08:54 - 17:05 (08:11)
reboot system boot 4.4.0-116-generi Sat Mar 31 05:33 - 17:05 (11:32)
reboot system boot 4.4.0-116-generi Sat Mar 31 05:13 - 12:33 (07:20)
reboot system boot 4.4.0-116-generi Sat Mar 31 04:32 - 12:33 (08:00)
reboot system boot 4.4.0-112-generi Sat Mar 31 04:24 - 12:33 (08:08)
reboot system boot 4.4.0-116-generi Sat Mar 31 04:08 - 11:23 (07:15)
reboot system boot 4.4.0-116-generi Sat Mar 31 04:02 - 11:23 (07:21)
reboot system boot 4.4.0-116-generi Tue Mar 13 19:39 - 11:23 (17+15:44)
reboot system boot 4.4.0-116-generi Sat Mar 10 09:32 - 11:23 (21+00:51)
reboot system boot 4.4.0-116-generi Sat Mar 10 04:09 - 16:48 (12:38)
reboot system boot 4.4.0-116-generi Mon Mar 5 08:56 - 16:48 (5+07:51)
reboot system boot 4.4.0-116-generi Sat Mar 3 08:17 - 16:10 (2+07:53)
reboot system boot 4.4.0-116-generi Sat Mar 3 04:36 - 14:05 (09:29)

[Shepherd King (shellcat-zero)]

Apparently, I've had VirtualBox guest utilities installed on my host system which you are generally just supposed to run on the guest. This issue only occurred when the package was updated. After trial and error, I've found that the offending package is virtualbox-guest-x11:amd64 (5.1.34-dfsg-0ubuntu1.16.04.2), none of the other virtualbox-guest packages cause this problem.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.